Transparent heat-sealing film

ABSTRACT

A heat-stealing film having a baze of not more than 30% and having a sealant layer made of a resin composition which comprises from 50 to 100 wt % of the total of the following components (a) to (c); (a) from 5 to 50 wt % of a block copolymer of from 50 to 95 wt % of a styrene-type hydrocarbon and from 5 to 50 wt % of a conjugated diene-type hydrocarbon, (b) from 5 to 50 wt % of an ethylene/α-olefin random copolymer, and (c) from 5 to 70 wt % of a block copolymer of from 10 to 50 wt % of a styrene-type hydrocarbon and from 50 to 90 wt % of a conjugated diene-type hydrocarbon, and (d) from 0 to 50 wt % of and impact-resistant polystyrene.

TECHNICAL FIELD

The present invention relates to a heat-sealing film to be used for apackaging container, particularly to a transparent heat-sealing filmhaving a sealant layer made of a heat sealable resin composition, and aprocess for its production. Such a heat-sealing film is also called acover film and is employed as a cover material for a plastic container,particularly a carrier container accommodating an electronic component.

BACKGROUND ART

A heat-sealing film for sealing a container made of e.g. plastic orpaper, is used also as a cover film which is a cover material forpackaging an electronic component, as represented, for example, by acarrier tape.

Such a heat-sealing film may be one having a two layer structurecomprising a stretched film to maintain tear strength and break strengthand to provide heat resistance for heat-sealing and a heat-sealing layerto present a fusion bonding property by heating. However, one having athree layer structure or a higher multilayer structure having aninterlayer disposed between the stretched film and the heat-sealinglayer, to provide an improvement of the mechanical strength, etc., iswidely used. Such a cover film having a three layer or higher multilayerstructure is produced by an extrusion-laminating method by utilizing theheat-sealing property of the heat-sealing layer or the interlayerinterposed between the heat-sealing layer and the stretched film.However, by this method, the number of extrusion-laminating stepsincreases as the number of layers increases, whereby there will be aproblem such that the productivity deteriorates, or the raw fabric lossincreases thereby to increase the cost. Also from the aspect of thequality of the product, the possibility of inclusion of foreign mattersincreases as the number of steps increases.

The heat-sealing film is required to have the following properties asthe basic properties:

(1) a heat-sealing property to readily obtain is practical peelstrength, and

(2) a readily openable property so that at the time of opening, thecontent can easily be taken out without scattering. In recent years, animprovement is desired also with respect to (3) transparency. If thetransparency is good, the packaged content can easily be ascertained,whereby the inspection operation may be facilitated, the reliability maybe improved, and reassurance may be obtained.

For example, JP-B-57-53828 or JP-B-57-42652 discloses a heat-sealingfilm which is excellent in the heat-sealing property and which isreadily openable. However, it does not necessarily fully satisfy therequirement for transparency. Accordingly, a heat-sealing film havingbetter transparency is required.

DISCLOSURE OF THE INVENTION

The present invention is intended to provide a heat-sealing filmexcellent in transparency without losing the basic properties of aheat-sealing film.

Further, the present invention relates to a process for producing aheat-sealing film which is inexpensive and constant in its quality, bysimplifying the process steps in the production of a multilayer film.

The present invention provides a heat-sealing film having a haze of notmore than 30% and having a sealant layer made of a resin compositionwhich comprises from 50 to 100 wt % of the total of the followingcomponents (a) to (c):

(a) from 5 to 50 wt % of a block copolymer of from 50 to 95 wt % of astyrene-type hydrocarbon and from 5 to 50 wt % of a conjugateddiene-type hydrocarbon,

(b) from 5 to 50 wt % of an ethylene/α-olefin random copolymer, and

(c) from 5 to 70 wt % of a block copolymer of from 10 to 50 wt % of astyrene-type hydrocarbon and from 50 to 90 wt % of a conjugateddiene-type hydrocarbon, and

(d) from 0 to 50 wt % of an impact-resistant polystyrene.

The styrene-type hydrocarbon to be used in the present invention may,for example, be styrene, α-methylstyrene and various alkyl-substitutedstyrenes. Among them, styrene is preferably employed. The conjugateddiene-type hydrocarbon may, for example, be isoprene, butadiene or onehaving hydrogen added to such an unsaturated bond portion. Among suchblock copolymers of from 50 to 95 wt % of a styrene-type hydrocarbon andfrom 5 to 50 wt % of a conjugated diene-type hydrocarbon, one type maybe used for each of components (a) and (c), but two or more types mayalso be used in combination. The α-olefin in the ethylene/α-olefinrandom copolymer may, for example, be propylene, butene, pentene orhexene.

The impact-resistant polystyrene comprises a tyrene-type hydrocarbonpolymer and a conjugated diene-type hydrocarbon polymer in such a mannerthat soft component particles made of the conjugated diene-typehydrocarbon polymer are dispersed in the styrene-type hydrocarbonpolymer constituting a matrix.

The block copolymer of a styrene-type hydrocarbon and a conjugateddiene-type hydrocarbon, the ethylene/α-olefin random copolymer and theimpact-resistant polystyrene may, respectively, be commercial products.

The mixing ratio of the resin composition comprising components (a) to(d) is such that component (a) is from 5 to 50 wt %, component (b) isfrom 5 to 50 wt % and (c) is from 5 to 70 wt %, provided that the totalamount of components (a) to (c) is from 50 to 100 wt %, and component(d) is from 0 to 50 wt %.

If component (a) is less than 5 wt %, film-forming tends to bedifficult, and if it exceeds 50 wt %, the temperature dependency of thepeel strength tends to be remarkable, and the readily openable propertytends to be impaired.

If component (b) is less than 5 wt %, no adequate peel strength tends tobe obtained, and if it exceeds 50 wt %, adhesion to rolls duringfilm-formation tends to increase, whereby the film-forming tends to bedifficult.

If component (c) is less than 5 wt %, it tends to be difficult to obtaina sealing condition required to impart the readily openable property,and if it exceeds 70 wt %, film-forming tends to be difficult.

If component (d) exceeds 50 wt %, the transparency tends to be hardlyobtainable.

The haze is an index for the degree of an opaque fogging state and isrepresented by a percentage of diffuse transmittance/total lighttransmittance when the diffuse transmittance and the total lighttransmittance are measured by means of an integrating sphere type lighttransmittance measuring apparatus. If the transparency is excellent, thediffuse transmittance will be small, and the smaller the haze value, thebetter the transmittance. The heat-sealing film of the present inventionhas a haze of not more than 30% and is excellent in transparency,whereby a packed content can easily be ascertained.

The thickness of the sealant layer is preferably less than 30 μm, morepreferably from 4 μm to 25 μm. With a heat-sealing film having a sealantlayer with a thickness of at least 30 μm, the transparency tends to below, and the visual image of transparency tends to be impaired.

The heat-sealing film of the present invention is most preferablyemployed in such a construction that the biaxially stretchedpolyethylene terephthalate layer constitutes the outermost layer, thepolyethylene resin layer constitutes the second layer in contact withthe outermost layer, and the polyolefin type resin layer constitutes thethird layer in contact with the second layer, and the above-mentionedsealant layer constitutes the fourth layer in contact with the thirdlayer.

As the biaxially oriented polyethylene terephthalate to be used for thebiaxially oriented polyethylene terephthalate layer, not only one whichis commonly used, but also one having an antistatic agent coated orkneaded for antistatic treatment or having corona treatment, etc.applied, may be employed.

For the polyethylene resin layer, low density polyethylene, linear lowdensity polyethylene or ultralow density polyethylene may, for example,be employed, and these polyethylenes may be used alone or in combinationas a mixture of two or more of them. Further, ethylene-1-butene, acopolymer of ethylene with a vinyl group having a carboxyl group, suchas an ethylene/acrylate or ethylene/vinyl acetate copolymer, or a threecomponent copolymer thereof with an acid anhydride, may be blended foruse.

To provide adequate bond strength between the outermost layer and thesecond layer, various anchor coating agents or surface treatingtechniques which are commonly employed, may be used. As an anchorcoating agent, a two part curable isocyanate type anchor coating agentmay be employed especially for enhancing the adhesion between thebiaxially oriented polyethylene terephthalate and the polyethyleneresin. Further, in order to enhance the adhesion between the anchorcoating agent and the biaxially oriented polyethylene terephthalatefilm, corona treatment may be applied to the biaxially orientedpolyethylene terephthalate film side, and ozone treatment may be appliedto the polyethylene resin side.

The polyolefin resin to be used for the polyolefin type resin layer may,for example, be an ethylene/1-butene copolymer, an ethylene/vinylacetate copolymer, an ethylene/acrylate copolymer, an ethylene/maleicacid copolymer, a styrene/ethylene graft copolymer, a styrene/propylenegraft copolymer, a styrene/ethylene/butadiene block copolymer, apropylene polymer, an ethylene polymer, or a blend product thereof.

The heat-sealing film obtained by the present invention may have atleast one side treated by antistatic treatment. The antistatic treatmentmay be carried out by coating a surfactant type antistatic agent, apolymer type antistatic agent or a conductive agent, as an antistaticagent, by spraying or by a roll coater employing e.g. a gravure roll.

The heat-sealing film comprising a biaxially oriented polyethyleneterephthalate layer as the outermost layer, a polyethylene resin layeras the second layer, a polyolefin type resin layer as the third layerand the sealant layer as the fourth layer, can be produced by a processwhich comprises a step of coating an AC agent on the biaxially orientedpolyethylene terephthalate film of the outermost layer, a step ofextrusion-coating the polyethylene resin of the second layer, and a stepof coextrusion-coating the polyolefin type resin layer of the thirdlayer and the sealant layer of the fourth layer.

Otherwise, it can also be produced by a process which comprises a stepof coating an AC agent on the biaxially oriented polyethyleneterephthalate film of the outer-most layer, and a step ofextrusion-laminating a coextruded film comprising the polyolefin typeresin layer of the third layer and the sealant layer of the fourthlayer, via the polyethylene resin of the second layer.

The resins and the resin composition to be used for the sealant layermay, for example, be high density polyethylene, low densitypolyethylene, linear low density polyethylene, polypropylene,polybutene-1, poly-4-methylpentene-1, an ethylene/propylene copolymer,an ethylene-1-butene copolymer, an ethylene/vinyl acetate copolymer, anethylene/acrylate copolymer, a styrene/butadiene copolymer and itshydrogenated product, a thermoplastic polyurethane, and a blend productthereof. Preferred is a resin composition which comprises from 50 to 100wt % of a mixture comprising:

(a) from 5 to 50 wt % of a block copolymer of from 50 to 95 wt % of astyrene-type hydrocarbon and from 5 to 50 wt % of a conjugateddiene-type hydrocarbon,

(b) from 5 to 50 wt % of an ethylene/α-olefin random copolymer, and

(c) from 5 to 70 wt % of a block copolymer of from 10 to 50 wt % of astyrene-type hydrocarbon and from 50 to 90 wt % of a conjugateddiene-type hydrocarbon, and

(d) from 0 to 50 wt % of an impact-resistant polystyrene.

As a machine for the production by the present invention, a commonlaminator may be employed, and a tandem laminator may preferably beemployed. As a coater to coat an AC agent to the biaxially orientedpolyethylene terephthalate film, a commonly employed coater such as aroll coater, a gravure coater, a reverse roll coater, a bar coater or adie coater, may, for example, be employed.

A T-die may be employed as a die for the laminator which extrudes thepolyethylene resin. Further, it may be provided with a dicker to adjustthe film width.

The laminator die for coextrusion of the polyolefin-type resin layer andthe sealant layer may, for example, be a T-die provided with a feedblock which is commonly used for coextrusion, a multi manifold die or adual slot die.

The polyolefin-type resin layer of the third layer and the sealant layerof the fourth layer may be formed into a double layer film by acoextrusion method. Especially, by a method of obtaining a double layerfilm by a T-die method, the molten resin discharged from the die will benipped by specular rolls, whereby the transparency will be increased. Ifit is attempted to obtain a single layer film of the sealant layer only,as the thickness is less than 30 μm in the present invention, it tendsto be difficult to attain a good thin thickness accuracy or to attainadequate peel strength constantly, whereby the transparency tends to beirregular. Whereas, by the coextrusion with the olefin-type resin, it ispossible to obtain a sealant layer having a constant thickness. Theobtained double layer film can be laminated with the biaxially orientedpolyethylene terephthalate layer via a molten polyethylene resin layeras the second layer, to obtain a heat-sealing film.

In the present invention, in addition to the above steps, a step ofantistatic treatment may further be added, as the case requires. As anantistatic agent, a surfactant type antistatic agent, a polymer typeantistatic agent or a conductive agent, may, for example, be coated byspraying or by a roll coater employing a gravure roll. Further, in orderto apply such an antistatic agent uniformly, the film surface maypreferably be treated by corona treatment or ozone treatment,particularly preferably by corona discharge treatment, prior to theantistatic treatment.

The heat-sealing film of the present invention may be used for a covertape for a carrier tape for a packaged electronic component or a carrierbag for an electronic component, which has functions to protect anelectronic component from pollution during the storage, transportationor mounting and to align and take out the electronic component to mountit on an electronic circuit board.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in further detail withreference to Examples and Comparative Examples.

EXAMPLES 1 TO 6

For a heat-sealing resin mixture (for a sealant layer), (a) astyrene/butadiene block copolymer resin (“Denka Clearene”, manufacturedby Denki Kagaku Kogyo K.K., styrene content: 80 wt %, butadiene content:20 wt %), (b) an ethylene/butene-1 random copolymer (“Toughmer A”,manufactured by Mitsui Chemical Co., Ltd.), (c) a styrene/butadieneblock copolymer (“STR resin”, manufactured by Nippon Synthetic RubberCo., Ltd., styrene content: 40 wt %, butadiene content: 60 wt %) and (d)an impact-resistant polystyrene resin (“Denka Styrol HI-E6”,manufactured by Denki Kagaku Kogyo K.K.) were manually blended to have acomposition as identified in Table 1 and compounded by a 40 mm singlescrew extruder at 200° C. to obtain a resin composition.

This resin composition and low density polyethylene as a polyolefin typeresin were subjected to coextrusion by a T-die method to obtain a doublelayer film (total thickness: 30 μm) having a sealant layer thickness asidentified in Table 2. This double layer film was laminated with abiaxially oriented polyethylene terephthalate film (thickness: 12 μm)via a polyethylene resin (thickness: 15 μm) by an extrusion-laminatingmethod to obtain a heat-sealing film.

COMPARATIVE EXAMPLES 1 to 5

In the same manner as described above, components (a) to (d) wereblended to have a composition as identified in Table 1 to obtain aheat-sealing resin mixture. Then, the mixture was coextruded with lowdensity polyethylene to obtain a film having a thickness as identifiedin Table 2, which was laminated with a biaxially oriented polyethyleneterephthalate film by a dry laminating method to obtain a transparentlaminated heat-sealing film (total thickness: 30 μm except forComparative Example 5 wherein the total thickness was 40 μm).

The following evaluations were carried out with respect to the filmsthus obtained.

Evaluation of Transparency (Measurement of Haze)

The haze was measured by means of an integrating sphere type measuringapparatus specified in Measurement Method A in accordance with JIS K7105(1998). The unit is %. The results are shown in Table 2.

Evaluation of Heat-sealing Property and Readily Openable Property

A heat-sealing film was sealed on a polystyrene type carrier tape forelectronic packaging material at 150° C. under conditions such that theseal head width was 0.5 mm×2, the sealing pressure was 0.4 MPa and thesealing speed was 2 times/sec. One having an average peel strengthwithin a range of from 0.2N to 0.6N was identified with symbol ∘, andone having an average peel strength outside the range was identifiedwith symbol X. The results are shown in the column for “Heat-sealingproperty” in Table 2. Further, one having a difference between themaximum value and the minimum value of peel strength of at most 0.4N,was identified with symbol ∘, and one having the difference outside sucha range, was identified with symbol X. The results are shown in thecolumn for “Readily openable property” in Table 2.

TABLE 1 Composition Resin composition No. (a) (b) (c) (a) + (b) + (c)(a) + (b) + (c) (d) 1 45 25 30 100 90 10 2 5 45 50 100 55 45 3 28 7 65100 70 30 4 45 45 10 100 100 0 5 55 25 20 100 90 10 6 20 60 20 100 90 107 15 10 75 100 90 10 8 45 25 30 100 40 60

TABLE 2 Thickness Heat- Readily Composition of sealant sealing openableHaze No. layer (μm) property property (%) Example 1 1 10 ◯ ◯ 13 Example2 2 10 ◯ ◯ 25 Example 3 3 10 ◯ ◯ 28 Example 4 4 10 ◯ ◯ 14 Example 5 1 25◯ ◯ 22 Example 6 1 4 ◯ ◯ 8 Comp. Ex. 1 5 10 ◯ X 14 Comp. Ex. 2 6 10 — —— Comp. Ex. 3 7 10 — — — Comp. Ex. 4 8 10 ◯ ◯ 45 Comp. Ex. 5 1 35 ◯ ◯ 32Note: Symbol — indicates that measurements were impossible due to toomuch fluctuations in thickness.

The heat-sealing films of Examples were heat-sealing films excellent intransparency without losing the basic characteristics such that they areexcellent in the heat-sealing property to readily obtain practical peelstrength and have a readily openable property whereby the content caneasily be taken out without scattering at the time of opening.

EXAMPLE 7

Preparation of a Polystyrene Type Resin for the Sealant Layer

(a) A styrene/butadiene block copolymer resin (Denka Clearene,tradename, manufactured by Denki Kagaku Kogyo K.K., styrene content: 80wt %, butadiene content: 20 wt %), (b) an ethylene/butene-1 randomcopolymer (“Toughmer A”, tradename, manufactured by Mitsui Chemical Co.,Ltd.), (c) a styrene/butadiene block copolymer resin (“STR resin”,tradename, manufactured by Nippon Synthetic Rubber Co., Ltd., styrenecontent: 40 wt %, butadiene content: 80 wt %) and (d) animpact-resistant polystyrene resin (“Denka Styrol HI-E6”, tradename,manufactured by Denki Kagaku Kogyo K.K.) were blended in proportions of40, 25, 25 and 10 wt %, respectively, and melt-kneaded by a 40 mm singlescrew extruder at a temperature of 200° C. to obtain resin pellets forthe desired sealant layer.

By means of a tandem laminator, a biaxially oriented polyethyleneterephthalate film (Toyobo Ester Film, tradename, manufactured by ToyoBoseki K.K., thickness: 16 μm) was supplied, and an isocyanate type twopart curable AC agent (“Takelac A971, Takenate A3”, tradename,manufactured by Takeda Chemical Industries, Co., Ltd.) was coated by anAC coater and dried to obtain a coated film, which was coated with a lowdensity polyethylene resin (“Novatec LD”, tradename, manufactured byNippon Polychem K.K.) extruded at a temperature of 320° C. by a 65 mmextrusion laminator provided with a T-die, in a thickness of 13 μm.Further, on this film, a low density polyethylene (“UBE Polyethylene”,tradename, manufactured by Ube Kosan K.K.) and the polystyrene typeresin for the sealant layer prepared as described above, werecoextrusion-coated at a temperature of 230° C. by a 65 mm extrusionlaminator provided with a multi manifold die, so that the thicknesses ofthe polyethylene and the polystyrene type resin would be 30 and 10 μm,respectively, to obtain a four-layer heat-sealing film.

EXAMPLE 8

By means of a tandem laminator, a biaxially oriented polyethyleneterephthalate film (“Toyobo Ester film”, tradename, manufactured by ToyoBoseki K.K., thickness: 16 μm) was supplied, and an isocyanate type twopart curable AC agent (“Takelac A971, Takenate A3”, tradename,manufactured by Takeda Chemical Industries, Co., Ltd.) was coated by anAC coater and dried to obtain a coated film, which was then coated witha low density polyethylene resin (“Novatec LD”, tradename, manufacturedby Nippon Polychem K.K.) extruded at a temperature of 320° C. from a 65mm extrusion laminator provided with a T-die, in a thickness of 13 μm.Further, on this film, a low density polyethylene (“UBE Polyethylene”,tradename, manufactured by Ube Kosan K.K.) and the polystyrene typeresin for the sealant layer prepared as described above, werecoextrusion-coated at a temperature of 230° C. by a 65 mm extrusionlaminator provided with a multi manifold die, so that the thicknesses ofthe polyethylene and the polystyrene type resin would be 30 and 10 μm,respectively, to obtain a four-layer heat-sealing film. Then, the filmsurface was subjected to corona treatment by a corona treatment machine.Then, a surfactant type antistatic agent (“SAT-4”, tradename,manufactured by Nippon Junyaku K.K.) was sprayed to obtain the desiredfilm.

EXAMPLE 9

By means of a tandem laminator, a biaxially oriented polyethyleneterephthalate film (“Toyobo Ester film”, tradename, manufactured by ToyoBoseki K.K., thickness: 16 μm) was supplied, and an isocyanate type twopart curable AC agent (“Takelac A971, Takenate A3”, tradename,manufactured by Takeda Chemical Industries, Co., Ltd.) was coated by anAC coater and dried to obtain a coated film. Whereas, a low densitypolyethylene (“UBE Polyethylene”, tradename, manufactured by Ube KosanK.K.) and the polystyrene type resin for the sealant layer prepared asdescribed above, were coextruded at a temperature of 230° C. by a 65 mmextrusion laminator provided with a multi manifold die, so that thethicknesses of the polyethylene and the polystyrene type resin would be30 and 10 μm, respectively, to obtain a coextruded film. Then, thecoated film and the coextruded film were extrusion-laminated via a lowdensity polyethylene resin (“Novatec LD”, tradename, manufactured byNippon Polychem K.K.) extruded at a temperature of 320° C. by a 65 mmextrusion laminator equipped with a T-die, so that the thickness of thepolyethylene resin would be 13 μm, to obtain a four-layer heat-sealingfilm.

EXAMPLE 10

By means of a tandem laminator, a biaxially oriented polyethyleneterephthalate film (“Toyobo Ester film”, tradename, manufactured by ToyoBoseki K.K., thickness: 16 μm) was supplied, and an isocyanate type twopart curable AC agent (“Takelac A971, Takenate A3”, tradename,manufactured by Takeda Chemical Industries, Co., Ltd.) was coated by anAC coater and dried to obtain a coated film. Whereas, a low densitypolyethylene (“UBE Polyethylene”, tradename, manufactured by Ube KosanK.K.) and the polystyrene type resin for the sealant layer prepared asdescribed above, were coextruded at a temperature of 230° C. by a 65 mmextrusion laminator provided with a multi manifold die, so that thethicknesses of the polyethylene and the polystyrene type resin would be30 and 10 μm, respectively, to obtain a coextruded film. Then, thecoated film and the coextruded film were extrusion-laminated via a lowdensity polyethylene resin (“Novatec LD”, tradename, manufactured byNippon Polychem K.K.) extruded at a s temperature of 320° C. by a 65 mmextrusion laminator provided with a T-die, so that the thickness of thepolyethylene resin would be 13 μm, to obtain a desired four-layerheat-sealing film. Then, the film surface was subjected to coronatreatment by a corona treatment machine, and then a surfactant typeantistatic agent (“SAT-4”, tradename, manufactured by Nippon JunyakuK.K.) was sprayed thereon to obtain a desired film.

According to the production processes of the above Examples, in theproduction of multilayer films, the process steps can be simplified, thenumber of operators can be reduced, and the low fabric loss can bereduced, thus contributing to reduction of costs, and further,heat-sealing films having constant quality, can be obtained.

1. A heat-sealing film which comprises a biaxially oriented polyethyleneterephthalate layer as the outer-most layer, a polyethylene resin layeras the second layer, a polyolefin type resin layer as the third layerand the sealant layer as the fourth layer, wherein (a) the polyethyleneresin layer is disposed between the polyethylene terephthalate layer andthe polyolefin type resin layer, and (b) the polyolefin type resin layeras being disposed between the polyethylene resin layer and the sealantlayer, wherein the first, second, third and fourth layers are differentand wherein the sealant layer is made of a resin composition comprisingfrom 50 to 100 wt % of the total of the following components (i) to(iv): (i) from 5 to 50 wt % of a block copolymer of from 50 to 95 wt %of a styrene-type hydrocarbon and from 5 to 50 wt % of a conjugateddiene-type hydrocarbon, (ii) from 5 to 50 wt % of an ethylene/α-olefinrandom copolymer, (iii) from 5 to 70 wt % of a block copolymer of from10 to 50 wt % of a styrene-type hydrocarbon and from 50 to 90 wt % of aconjugated diene-type hydrocarbon, and (iv) from 0 to 50 wt % of animpact-resistant polystyrene.
 2. The heat-sealing film according toclaim 1, which has antistatic treatment applied to at least one side. 3.A process for producing the heat-sealing film as defined in claim 1,which comprises a step of coating an AC agent on the biaxially orientedpolyethylene terephthalate film of the outer-most layer, a step ofextrusion-coating the polyethylene resin of the second layer, and a stepof coextrusion-coating the polyolefin type resin layer of the thirdlayer and the sealant layer of the fourth layer.
 4. A process forproducing the heat-sealing film as defined in claim 1, which comprises astep of coating an AC agent on the biaxially oriented polyethyleneterephthalate film of the outer-most layer, and a step ofextrusion-laminating a coextruded film comprising the polyolefin typeresin layer of the third layer and the sealant layer of the fourthlayer, via the polyethylene resin of the second layer.
 5. A process forproducing the heat-sealing film as defined in claim 2, which comprises astep of coating an AC agent on the biaxially oriented polyethyleneterephthalate film of the outer-most layer, a step of extrusion-coatingthe polyethylene resin of the second layer, a step ofcoextrusion-coating the polyolefin type resin layer of the third layerand the sealant layer of the fourth layer, and a step of applyingantistatic treatment to at least one of the biaxially orientedpolyethylene terephthalate layer surface and the sealant layer surface.6. A process for producing the heat-sealing film as defined in claim 2,which comprises a step of coating an AC agent on the biaxially orientedpolyethylene terephthalate film of the outer-most layer, a step ofextrusion-laminating a coextruded film comprising the polyolefin typeresin layer of the third layer and the sealant layer of the fourthlayer, via the polyethylene resin of the second layer, and a step ofapplying antistatic treatment to at least one of the biaxially orientedpolyethylene terephthalate layer surface and the sealant layer surface.7. The process for producing the heat-sealing film according to claim 5,wherein corona discharge treatment is applied to at least the surface tobe treated by antistatic treatment, prior to the step of applyingantistatic treatment.
 8. The process according to claim 3, wherein allsteps are carried out within one and the same line.
 9. The process forproducing the heat-sealing film according to claim 6, wherein coronadischarge treatment is applied to at least the surface to be treated byantistatic treatment, prior to the step of applying antistatictreatment.
 10. The process according to claim 4, wherein all steps arecarried out within one and the same line.
 11. The process according toclaim 5, wherein all steps are carried out within one and the same line.12. The process according to claim 6, wherein all steps are carried outwithin one and the same line.
 13. The process according to claim 7,wherein all steps are carried out within one and the same line.
 14. Theprocess according to claim 9, wherein all steps are carried out withinone and the same line.